1. Field of the Invention
The invention relates to a technique for correcting meandering of a web, which is a sheet-like continuous material, in an apparatus that transports the web.
2. Description of the Related Art
An apparatus that transports a web, such as a metal film or a plastic film, while supporting the web with a plurality of rollers has been suggested. In the above apparatus, the web meanders due to various reasons. Therefore, there is a need for a technique for correcting or preventing the meandering of the web.
The following related arts are disclosed as techniques for handling the meandering of the web. Japanese Patent Application Publication No. 2007-210747 (JP-A-2007-210747) describes a technique that a filter is provided to extract a variation in level of a signal output from an edge sensor in edge detection of a recording medium in an ink jet printer, or the like. According to JP-A-2007-210747, this can remove a component of an unnecessary frequency band from the signal output from the edge sensor.
Japanese Patent Application Publication No. 2003-182896 (JP-A-2003-182896) describes a technique that a low-pass filter is provided to remove a high-frequency component from a signal output from a processing unit that processes a signal output from an edge position detection sensor.
Japanese Patent Application Publication No. 11-40144 (JP-A-11-40144) describes a technique that an electrode material before reaching a winding machine is pinched by a pair of rotatable rollers from both sides and then an edge of the electrode material is adjusted by rotating the rollers on the basis of a detected edge position.
Japanese Patent Application Publication No. 9-208093 (JP-A-9-208093) describes a technique that a feeding position of a widthwise edge of a belt-like element is adjusted by moving a position of a feeding-side shaft in a widthwise direction of the belt-like element on the basis of the widthwise displacement of the belt-like element and the moving speed of the belt-like element.
As described in JP-A-2007-210747 or JP-A-2003-182896, in web meandering correction control, it is necessary to remove a high-frequency component from a signal detected by an edge sensor. This is because the high-frequency component includes noise that is not caused by meandering of a web but by an initial shape of an edge of a web, or the like. When web meandering correction control is executed in a feedback manner, or the like, to track that noise, inconvenience, such as oscillation, may occur. On the other hand, when meandering correction control is intended with high accuracy, it is necessary to acquire a feedback gain as much as possible. Thus, it is desirable to acquire a detection signal having a frequency band as wide as possible. In order to implement this, it is effective that, in a low-pass filtering process executed on a signal detected by an edge sensor, an upper limit frequency used as a reference for cutting off is set to the highest frequency possible within the range that does not include the high-frequency noise.
However, the upper limit frequency in the low-pass filtering process is normally fixed. For this reason, for example, even when there is substantially no high-frequency noise, a signal detected by an edge sensor is handled in a similar manner. In terms of this point, there is still room for improvement to implement meandering correction control with high accuracy.